Cassel knows and has stated the Pats gave him his chance, so I cannot see him upset over taking $14.6 million for one season knowing he would be up for the same signing bonus the next year (that one-year salary will provide a degree of security in the event of injury).
He has not displayed a Samuel-type personality, so I would be surprised if the quiet, humble one suddenly shifts to "get paid" mode. As a QB and an offensive/team leader, shaking the franchise to benefit yourself does not make yourself marketable, so I would be amazed if Cassel protested one year with the tag. If the Pats try to trade him and the team looking to trade for him demands restructuring (the franchise value is a pretty big number to eat and provides only a one-year promise before free agency), that would be where I expect Cassel to protest. At that point, the Pats are no longer his team and he is simply a commodity, protecting his own interests and not those of his former team looking only to get the most it can in exchange for him.